The zinc nutritional status of infants anf preschool children in the United States will be assessed in on-going studies. These will include the long-term evaluation of the effects of dietary zinc supplementation during infancy on zinc nutritional status, growth and development; a controlled study to evaluate the effect of dietary zinc supplementation on the growth of preschool children who have evidence of zinc depletion and low growth percentiles in comparison with the zinc nutritional status of preschool children from lower and upper-middle income families, and studies of the role of zinc deficiency in the pathogenesis of Acrodermatitis Enteropathica. Bibliographic references: Humbert, J.R., Hambidge, K.M., Moore, L., and Martinex, B.: Effect of various chemotactants in a new chemotaxis assay. Clin. Res., 23:151A, 1975; Walravens, P. A. and Hambidge, K.M: Supplementation of an infant milk formula with zinc. Am. J. Clin. Nutr., 1975.